International Conference on Control, Engineering & Information Technology (CEIT’14) Proceedings - Copyright IPCO-2014 ISSN 2356-5608
Switched Reluctance Machine For A Starter-Alternator Micro- Hybrid Car
Sihem Saidani, Moez Ghariani Laboratory of Electronics and Information Technology (LETI) Electric Vehicle and Power Electronics Group (VEEP) National School of Engineers of Sfax B.P. 1173 3038 Sfax Tunisia e-mail: [email protected] , [email protected]
ABSTRACT
Living in a world where environment protection and energy The following characteristics of the Switched Reluctance conservation are the first worries, the development of hybrid Machine [13] (SRM) had attracted researchers to investigate its vehicle seems to be an accelerated pace. There for, recent potential for variable speed applications: efforts are directed toward developing an improved -Simplified construction with rotor consisting only a propulsion system. One of the most valuable solutions is the laminated steel starter alternators [19]. This paper presents an advanced -Concentrated phase winding for only on the stator poles development of a switched reluctance starter-alternator for a (independent phases command) micro-hybrid vehicle. The performance, efficiency and torque -Absence of permanent magnet, which gives high cost and low characteristics of switched reluctance machines combined manufacturing with its robust, low cost construction makes that technology The fact of using a machine in such conditions, we can operate an interesting alternative to other machine types chosen for at high speed and high temperature operation since the rotor traction applications especially starter/generator. This paper can act as a cooling source to the stator as higher reliability will provide an overview of the present status of hybrid since each phase is electrically and magnetically independent. vehicles worldwide and their state of the art, with emphasis For the first time we will describe the technology of hybrid on the engineering philosophy and key technologies. Using vehicle and the use of starter alternator system. Next , we the Finite element method by the program FEMM we also As known; the finite element method (FEM) has been a present a model of switched reluctance machine 12/8 powerful tool to solve many complex problems in proposed for starter-alternator application. electromagnetic especially for modeling machines. For the Keywords —Hybrid Vehicle, Starter-Alternator, Switched optimum design of switched reluctance motors, this paper Reluctance Machine, FEMM. presents the methods and results, which are calculated by the finite element analysis. First, the geometry and mechanical I. INTRODUCTION parameters of the machine are established, when a finite- element modeling (FEM) approach is initially developed to The necessity to decrease fuel emissions and improve fuel obtain the flux linkage/current/rotor position relationship so economy of cars requires a big change in conventional that the proper and mutual inductances and also its torque and structure used[20]. There for , the automotive industry has field distribution characteristics can then be computed. been investigating alternatives to conventional internal combustion engine powered vehicles in order to improve II. HYBRID VEHICLE their fuel efficiency and to reduce their greenhouse gas emissions. In several instances, electric machines are A hybrid electric vehicle is the kind of vehicle which integrated into the power train for the sole purpose of combines conventional propulsion system, such as an internal optimizing the energy delivery and recovery during vehicle combustion engine (ICE) and an electric propulsion system propulsion. Hybrid electric vehicles are a key-piece of the with a rechargeable energy storage system, such as batteries . future of the automotive industry. It has been demonstrated Thus, Fuel consumption is minimized by turning off the that Hybrid Vehicle (HV) offers benefits to fuel consumption, internal combustion engine during idle and low of the car; we durability, and drivability to the end-user. The most realized can recapture energy through regenerative breaking, which version of the HV is the starter/alternator coupled to the converts a portion of the vehicle’s kinetic energy into internal combustion engine [10]. electrical energy during breaking and stop events. These The starter generator replaces the conventional starter motor benefits lead to improved durability of the engine as a whole and the alternator (generator). It provides, beside its two basic due to elimination of the strain on the internal combustion functions (starter and alternator), an auxiliary one, as a engine during idle events and braking [10]. The use of HV convenient automatic vehicle start-stop system for further benefits the environment by reducing emissions, caused by improved fuel efficiency.[11] reducing fuel consumption, and reducing noise pollution, by
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International Conference on Control, Engineering & Information Technology (CEIT’14) Proceedings - Copyright IPCO-2014 ISSN 2356-5608 using the electric motor at low speeds. Hybrid power trains The concept of starter-alternator to the flywheel has been use a conventional ICE in combination with an electric forwarded over the past several years. It is intended to motor, a battery, and an electronic controller. provide the following functions: HV have two basic configurations: series and parallel -Starter for the thermal engine hybrids. In the series variant, the ICE is used to drive an alternator to -Generator for charging the car battery and supplying the on generate electricity stored then in a battery system or sent board equipment directly to the electric motor in order to power the wheels. The efficiency of the engine is maximized because it operates -Acceleration assisting for the thermal engine within a narrow range of speeds. . Despite, the parallel hybrid vehicle has two power paths, so that either the IEC or the -Stop and go function to minimize the polluting emissions in electric motor (or both) can be used to power the wheels urban traffic. directly. Like the series configuration, it can operate in zero- Because of their robustness, low price, good efficiency , high emission mode (power supplied solely via the electric torque and speed capability, the doubly salient switched motor).The Fig.1 describes the basic configurations of HV: reluctance machines seems to be a good choice in comparison to classical synchronous or asynchronous machines for such application. III. MOTOR SELECTION
The electric motor of a starter alternator system is desired to have a high starting torque for initial acceleration and then and high efficiency to extend the battery range and a wide operating speed range as generator. Some motors types have the inherent property of operating with large extended speeds such as excited dc motors is an but its the principal problems especially the commutators and brushes, that limit the maximum speed of the motor and create sparks which require expected maintenance. With development of the power electronics and microprocessors, the frequency variable inverter/converter makes multiphase AC machines dominate the starter alternator system applications. Many types of machines have been used such as claw pole Lundell machine, induction Fig . 1. The basic configurations of HV machine, switched reluctance machine, permanent magnet machines. As the electric motor and the battery provide additional power to the ICE, the fuel consumption is reduced without III.1 The Lundell claw-pole machines affecting power output. To further save fuel, the engine automatically stops when the vehicle comes to a stop, and Having the same operating principle, the Lundell machine starts again automatically when the accelerator is depressed. are synchronous machines. The stator is similar to other The battery is recharged using the energy captured during multiphase AC machines and a rotor consists of claw pole regenerative braking, relieving the IEC of doing all that work, segments .The Lundell claw-pole machines are widely used and saving more fuel. A hybrid power train is completely as alternators in the automotive industry. The air gap flux self-sufficient, it doesn't need to be plugged in and charged can be adjusted by controlling field current..The power up overnight. The mild hybrid cars are operated in a same limitation (up to 2.5Kw AT 5000rpm) is caused by high- manner as the full hybrids. Unlike a full hybrid, a mild hybrid rotor leakage flux between claw poles when the axial- has a much smaller battery than a full hybrid and cannot run lamination length is increased. The classical Lundell on battery power alone.[12] machines still suffers from a power electromechanical efficiency, skin effect and high losses. Next , a comparison Clearly, a less expensive hybrid system is more likely to between other types of machines will show that starter- appeal to a greater number of mainstream consumers than alternator application needs induction machine, permanent would more robust and more expensive hybrid systems, at magnet and especially switched reluctance motors. [17] least in the initial phases of market development. As consumers gain a greater understanding of the differences in hybrid technologies, they will be better able to match their need for increased fuel mileage with the most cost-effective system. [21]
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International Conference on Control, Engineering & Information Technology (CEIT’14) Proceedings - Copyright IPCO-2014 ISSN 2356-5608
Fig.3 Induction Machine (IM) Fig.1 Lundell machine with dual field coils
The induction machine is allowed to run at the slip values III.2 Permanent Magnet Machines corresponding to the maximum torques with frequency variation during cranking procedure because the cranking The PM is a synchronous machine having the most efficient procedure is very short (0.2~3s). But the slip at the maximum (due to the absence of field-coil losses) but the highest cost torque causes low power factor and high machine losses than the others motors used in drive applications. The PM has .Thus, high reliability and low technological risk will make it tow types a surface-mounted Pm and interior PM (IPM) the primary technology in the near future. which is better suited for starter alternator applications. The IPM machine can be can be used with Ld
The rotor is so simple: without any windings or magnets, and is usually made by steel laminations in order to minimize the core losses. The SRM a is machine suited for harsh environments. Thus, the torque ripple, vibration, and acoustic noise are the most disadvantages of the SRM. The acoustic noise in SRMs are caused by the radial forces that increase inversely with the air gap and especially when the force frequency is near the stator resonant frequency.[16] The switched reluctance machine is excited by current pulses applied independently to each phase. The current
pulses are applied on precise rotor position and the motor Fig.2 Interior Permanent Machine creates torque in the direction of increasing inductance. In Fig.4, we represent :the torque is positive when dL/d >0 III.3 Induction Machine (IM) from 1 to 2, and the SRM so it is the motoring mode. shown in Fig.4.[17] The induction machine has a high efficiency and smooth torque which able it usually used like a three-phase candidate for starter alternator application throw a dc inverter/converter. Despite her size and compared to PM and SRM, the IM seems to have the lowest power and efficiency.
Fig.4 Inductance vs. rotor position angle
The torque ripple, vibration and acoustic noise are the most disadvantages of the SRM. The torque ripple can be reduced via controlling the current by the switching angles where we
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International Conference on Control, Engineering & Information Technology (CEIT’14) Proceedings - Copyright IPCO-2014 ISSN 2356-5608 include conduction angle, switching-on and –off position. A wide choice of pole configurations and phase numbers are possible with SRMs. Lower number of phases even it can reduce the converter cost, but it increases the torque ripple for example as three phases 12/8 poles is better than 3 phases 6/4 poles .
IV. FINITE-ELEMENT ANALYSIS OF SRM Determining the magnetic characteristics is the key of optimization and controlling a switched reluctance machine. We define next the method used and the
Fig.6 A double salient switched machine (12/8) IV.1 FINITE ELEMENT METHOD (FEM) We have to name air gap as “air” (Fig.7). Also it must be THE finite element method has become a practical method emphasized that in each phase input and outputs shown for solving electromagnetic problems. It has been one method (Fig.6) as A+, B+, C-, C+…[1]and the number of winding of the widely methods used to study the SR machines [1]. must also be written such as 10,50,…(12 in our cas:Fig.7) Thus, to simplify complex geometries such us motors, we Each part of the machine (Fig.7) are named according to the have to break down the problem into small regions (Fig. 5). metals used such as M–45 steel, stainless steel...( show in Fig.8) and the windings must also be marked as “coil” since the drawings.
Fig.5 triangulation of the SR machine
Many tools of finite elements have been developed last years in order to compute the accurate properties and magnetic characteristics of machine without constructing a real prototype. FEMME is a program that can solve electromagnetic problems on 2D (two –dimensional planar). Fig.7 A 12/8- pole switched reluctance machine Thus, we can resolve linear and nonlinear magnetostatic, harmonic magnetic, linear electrostatic and steady state heat The dimensions of the switched reluctance motor are next in problems. The determination of magnetic characteristics table 1. : facilitates the optimization and control of switched reluctance Table1.geometry of SR machine 12/8 machine. [3] In particular, the switched reluctance machine phase SR machine Model magnetization characteristics vary hardly as a function of both excitation current and rotor position. Thus, numerical Stator outer diameter 137(mm) methods must be used in order to calculate the magnetic field Stator inner diameter 85(mm) and to predict the magnetization characteristics.[4] Stator teeth length 22(mm)
IV.2 RESULTS Rotor outer diameter 42.48(mm) The switched reluctance machine has both salient poles in stator and rotor. Each phase has a number of combinations Air gap 0.325(mm) from those we choose 12/8. Every winding phase are Number of turns 12 mounted around stator poles diametrically opposite: A-A,B- Stator pole arc 30(°) B,C-C…( Fig.6 ). Rotor pole arc 45(°) Rotor teeth length 18.02(mm)
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International Conference on Control, Engineering & Information Technology (CEIT’14) Proceedings - Copyright IPCO-2014 ISSN 2356-5608
Fig.10 Inductance profiles for different currents Fig.8 Magnetization cure of 1010 Steel The SR machine has neither winding nor magnet on the rotor. The SR machine tends to operate on the minimum reluctance To control the operating mode of the switched machine law [2]. The torque is produced when we have an reluctance (motor or generator) we have to calculate the maximum Lmax variation among the magnetic circuit: the stator windings are and the minimum inductance Lmin using the relations: excited of voltage or current at each phase independently so that each tries to attract the closest rotor pole toward the Lmax =3/2Ld alignment of the poles. Lmin =3/2Lq The induction L( ɵ) is calculated by using the coenergy W stored of the machine given by the next equation:
W=1/2*L ( ɵ).i²
The inductance profile for on phase is shown in Fig. 9. The current excitation of the phases is synchronized with the inductance region for climbing positive (motoring) torque and with the decreasing inductance region (generating). [8]
Fig.11 Static Torque (phase A) for different current excitation
Looking at Fig.11, the torque is positive (motoring) between 0° and 22.5° and negative between 22.5 and 45°.We can use these result to control each operating mode. The simulation of the machine with alternative currents we represent next the flux distribution (Fig.12).
Fig. 9the idealized inductance profile
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[4] E. F. RYBICIU and M. F. RANNINEN, A finite element calculation of stress intensity factors by a modified crack closure integral, Engineering Fracture Mechanics , 1977, Vol 9,pp.931-938. [5] Hans Kuß, Torsten Wichert and Bernard Szymanski,Design of a high speed Switched Reluctance Motor for spindle drive,5 th International Conference-Workshop –CPE 2007 [6] Wei Cai, Senior Member, IEEE, Pragasen Pillay, Low- Vibration Design of Switched Reluctance Motors for Automotive Applications, IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL 09,JULY/AUGUST 2003. [7] Longya Xu, Eric Ruckstadter,Direct Modeling of Switched Reluctance Machine by Coupled Field - Circuit Method
ZHANG Wei,ZHANG Yingcha,LIU Yujuan, Simulation of Fig.12 The flux distribution due to an excitation of one phase Vector Control Sysetm of Induction Motors Base on Matlab, International Journal of Advancements in Computing Technology (IJACT) Volume4,Number8,May 2012. [8] Mehdi Dhaoui , Lasaas Sbita, A new Methods for Losses Minimization in IFOC Induction Motor Drives, International Journal of Systems Control (Vol.1-2010/Iss.2). [9] Jessica L. Colton, Design of an Integrated Starter-Alternator for Series Hybrid Electric Vehicle: A case Study in Axial Flux Permanent Magnet Machine Design,2010 . [10] M.BOUDOUDA,F.NACERI and A.HAMZAOUI,Simulation and Determination of the laws control of the SRM for the Integrated Starter Generator application,International Journal of Sciences and Techniques of Automatic control & computer engineering IJ-STA,Volume 2,N°1 July 2008. [11] Joseph Paul Porembsky, Control of Start and Stop events in a HEV, Ohio 2007. [12] STET,Cristian-VIOREL,Ioan-Adrian-SZABO,Lorand LOWENSTEIN, Lars, Hybrid Electric Vehicles Based On Switched Reluctance Motor Drives,
[13] Khwaja M. Rahman,Steven E. Schulz ,Design of High-Efficiency and Fig.13 The flux in air gap High-Torque-DensitySwitched Reluctance Motor for Vehicle Propulsion, IEE TRANSACTIONS ON INDUSTRY V. CONCLUSION APPLICATIONS, VOL.38. [14] Erich Shmidt,Comparison of Sycnronous Reluctance Machines with High-Anisotropy Rotors,CMP-177. This paper presented the use of the switched reluctance in [15] Acad. G. Bonchev, Parametric Analysis Of The PM Motor For Hybrd th hybrid vehicle as a starter alternator application. The control of Electric Vehicles,11 Nathiona Congress on Theoretical and Applied Mechanics ,2-5 Sept.2009. such machine leads to a study its electromagnetic [16] DORIN DUMITRU LUCACHE ,Survey of Some Automotive characteristics from its two-dimensional finite element method Integrated-Starter-Generators and their Control, 9th WSEAS using FEMM. The model of 12/8 SR machine will enable us in International Conference on AUTOMATION and the next work to develop a control strategy in a SIMULINK INFORMATION (ICAI'08), Bucharest, Romania, June 24-26, /MATLAB to optimize the characteristics of the alternator in 2008 ISBN: 978- order to avoid the acoustic noise produced by stator vibrations [17] Dr. William,CAI Comparison and Review of Electric in operating mode.[6] Machines for Integrated Starter Alternator Applications, IAS 2004 [18] John M. Miller, Patrick J. McCleer, Jeffrey H. Lang,Starter- VI. REFERENCES Alternator for Hybrid Electric Vehicle: Comparison of Induction and Variable Reluctance Machines and Drives. [1] DURMUSYYGUN,CANERAUNER,MEHMETYUMURTA [19] B. Fahimi, , Ali Emadi and Raymond B. SepeA Switched CI, A New Construction of Switched Reluctance Motor Reluctance Machine-Based Starter/Alternator for More Improving Magnetic Field Energy and Torque Production , Electric Cars, IEEE transactions on energy conversion, Vol. th Proceeding of the 6 SEAS International Conference on 19, No. 1, March 2004 Application of Electrical Engineering, Istanbul May 2007. [20] C. C. CHAN, The State of the Art of Electric and Hybrid [2] Wenzhe Lu,M.S.E.E,Modeling and control of switched Vehicles, Proceedings of the IEEE, Vol. 90, NO. 2, February reluctance machines for electro-mechanical brake 2002. systems,2005 [21] Geun-Ho Lee, Geo-Seung Choi and Woongchul Choi, Design [3] T.Jahan.M.B.B.Sharifian and M.R Feyzi, Static Considerations for Low Voltage Claw Pole Type Integrated Characteristics of Switched Reluctance Motor 6/4 By Finite Starter Generator (ISG) Systems, Journal of Power Element Analysis, Australian Journal of Basic and Applied Electronics, Vol. 11, No. 4, July 2011. Sciences,5(9):1403-1411,2011 ISSN 1991-8178.
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International Conference on Control, Engineering & Information Technology (CEIT’14) Proceedings - Copyright IPCO-2014 ISSN 2356-5608
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